1. Field of the Invention
This invention relates to mattresses, in particular, to the upholstery pad of a mattress with reinforced wire grid support.
2. Scope of the Prior Art
A conventional mattress generally consists of an innerspring with at least one upholstery layer, and a quilt panel portion. Typically, both the upholstery portion and the quilt panel portion in a mattress are made of layers of foam and fiber. The foam and fiber products provide the level of support and comfort of a mattress, referred to as its "firmness." The firmness of a mattress is a function of the foam and fiber layers in both the upholstery portion and the quilt panel portion as well as the performance characteristics of the innerspring.
In general, the innerspring consists of border wires which form a rectangular structure that surrounds a plurality of interconnected coil springs situated in rows and columns within the rectangular structure of the innerspring. The performance of an innerspring is a function of coil count, coil density, coil shape, the number of turns of the coil, the wire gauge, the heat treatment of the wire, the assembling technique, and the edge treatment, among other factors. These characteristics of the innerspring should be taken into consideration when designing an innerspring.
The layers of foam and fiber that make up the upholstery portion are adjacent to the top and bottom surfaces of the innerspring. The upholstery portion generally consists of an insulating layer of material next to the innerspring and a layer of padding. The insulating layer satisfies two purposes: it masks or insulates the noise produced by the interaction between the coils of the innerspring, and it prevents the softer upholstery materials from falling into the pockets of the innerspring. The insulating layer may be constructed of a wire mesh, a plastic mesh, or woven or non-woven material. Adjacent to the insulating layer is a layer of padding material which affects the firmness of a mattress. This layer may be constructed of natural fibers, such as cotton, synthetic fibers, foam, or any combination of these. Additional layers of padding may also be provided in the upholstery portion, thereby increasing the comfort level and the quality of the mattress.
The outermost part of the mattress is the quilt panel portion which is adjacent to the top and bottom upholstery portions. The quilt panel portion comes in direct contact with the sleeper and thus provides the perception of softness or feel. The quilt panel portion typically consists of a layer of mesh or cloth backing material, a layer of foam material positioned over the backing material, a layer of fiber or filler material on top of the foam and finally, a ticking layer forming the cover of the mattress. The level of comfort provided by the mattress and the quality and expense of the mattress is a function of the number and characteristics of foam and filler layers in the quilt panel portion. The quilt panel portion is so-named because the layers are stitched together with thread to form a quilt pattern. This stitching holds the layers together and provides a composite structure to the quilt panel portion.
More recently, mattresses have been improved by the addition of a firmer edge of the mattress as described in U.S. Pat. No. 5,704,085. Past approaches for increasing the strength of the edge of the innerspring were ineffective when more and thicker layers of upholstery and quilt panel portions were added. The support about the outer edge of the mattress disclosed in the '085 patent reduced sagging effect of the mattress when a sleeper sits on the edge of the bed. This edge support also allowed for more and thicker upholstery layers. Therefore, the '085 patent addressed the problems of past approaches by providing an edge support in the upholstery of the mattress.
While the invention of the '085 patent addressed the problems with edge support in mattresses with thicker upholstery and quilt panel portions, the problems associated with diminished innerspring support with thicker upholstery remained. Additionally, the support described in the '085 patent on its own only provided a strong support at the edge of the mattress; the additional firmness was not felt throughout the expanse of the mattress. Thus, a mattress embodying only the improvement disclosed in the '085 patent created a pocket of softness within the central portion of the mattress. For sleepers who prefer a firm bed, that was not a desired result.
The firmness of a mattress is measured by its indentation force deflection (IFD). Typically the foam in a mattress is 20-40 IFD, which is considered relatively soft. Traditionally, foams with a greater IFD were not used, as such firmness in a mattress was generally not considered comfortable. As mattresses became thicker and softer, the support provided by a standard mattress declined as a result of sagging upholstery and quilt panel portions. Past approaches attempted to remedy this problem by, for example, incorporating an anti-sagging means into the upholstery. Those approaches proved unsuccessful. Until the present invention, nothing in the prior art suggested the use or claimed the benefits of a wire grid in the upholstery of a mattress. In U.S. Pat. No. 3,317,274 to Upton, for example, the sag-resistant insert was constructed of foam rubber slabs and an aluminum stiffening portion. That insert was placed between a mattress and a box spring. In other words, Upton teaches a separate component that is completely detached from the innerspring assembly. U.S. Pat. No. 3,751,742 to Worley, disclosed a mattress filler composed of resilient foam that can be added to a mattress that had lost its supporting characteristics through use. The purpose of the mattress filler was to re-establish the original comfort of a used mattress. Finally, U.S. Pat. No. 2,174,711 to Walker disclosed the use of steel bands in parallel relation between the padding. The invention of the '711 patent, however, did not remedy the problem of sagging; it simply provided a barrier against the helical springs. Moreover, nothing in the prior art suggested the use of firmer foam as a supporting means in the upholstery. Instead the prior art assumed that every sleeper preferred a softer upholstery in the mattress, and thus the industry typically used 20-40 IFD foam.
Thus, there is a need for additional support in the upholstery portion in thicker mattresses to compensate for the sagging and loss of support of the innerspring. There is a further need for a firm foam support in the upholstery portion to rectify the problem of a soft pocket within the central region of the mattress. Additionally, the structure provided for additional support should not require additional and separate components to be purchased by the end user.